This invention relates to a flow control means useful in an apparatus for forming a non-woven fibrous web. More specifically, the invention relates to a device for forming a uniform density dispersion of fibers from a slurry of fibers and for depositing the dispersion onto a web former.
The control of a stream of fibers, first non-uniformly suspended in an aqueous slurry and then uniformly suspended throughout a dispersion, is of great importance in the manufacture of web-formed non-wovens. The fiber slurry, which is generally confined in a circular conduit, is usually delivered to a means for converting the slurry into a dispersion by a suitable pump. It is then necessary to transform the slurry into a dispersion and deliver the dispersion to the web forming region of the non-wovens manufacturing apparatus in the form of a wide and relatively shallow stream having a generally rectangular cross section, which stream may be under considerable pressure.
It is known that to produce a non-woven web having uniform physical properties, the stream of fibers in a dispersion delivered to the web forming region of the apparatus should be evenly distributed across the web former. This means that the energy of the stream delivered to the web former should be as uniform as possible throughout the stream cross section, and in addition, the entire stream should be maintained in a condition which is as near to steady-state flow as possible. In other words, the stream should be delivered to the web former at a uniform pressure and velocity across the width of the former, and the pressure and velocity relationship should be substantially invariant.
A web former, in the case of a Fourdrinier machine, generally is a continuously travelling, endless wire, having a horizontally extending run through which (by means including capillary action and surface tension) the medium in which the fibers are dispersed is drawn through so as to leave upon the upper surface of the wire a web of fibers.
The need is well understood and accepted in non-wovens manufacture to supply each incremental area of the web former with an equal and uniform distribution of fibers in dispersion, under steady-state flow conditions, in the form of a moving mass of medium and fiber, with each layer thereof moving in the machine direction at the same velocity and under a pressure that allows a delivery velocity substantially equal to the speed of the moving web former. Various flow control means have been suggested and used in an effort to attain these conditions, but none have been altogether satisfactory.
One known flow control means has utilized multiple feeds of individual fiber streams through a head box to the web former by means of small conduits positioned perpendicular to and across the width of the head box and former, the streams normally being piped into the small conduits through a single, large circular conduit. However, in this event each small conduit creates its own currents and turbulences, which does not produce the uniform pressure and velocity in the composite stream that eventually is delivered onto the web former.
Also, in the manufacture of non-wovens, it has been found that long crimped, synthetic fibers cannot be dispersed by methods used for the dispersion of short crimped or straight fibers. The present invention has been found to be particularly useful for forming a dispersion of fibers of 1.5 denier having a length of about 2 inches, whereas the prior art methods and apparatus are generally useful only for dispersion of fibers about a maximum of 1/2 inch in length. The present invention is particularly useful for forming a dispersion of long crimped fibers in a high viscosity medium and transferring the dispersion as a three-dimensional loosely entangled fiber network to the web former so that it may be formed into a non-woven web. Previously, during the process of transferring such a fiber dispersion to the web former by conventional means, such as the conduits mentioned above, the integrity, i.e. the degree, uniformity, and three-dimensional characteristics, of the dispersion were susceptible to damage.
Thus, an object of this invention is to form a uniform density dispersion of fibers in a slurry and deliver the dispersion intact to a web former.
Another object of this invention is to provide means particularly for uniformly dispersing fibers previously found to be difficult to disperse and for delivering such a dispersion to a web former in a condition where the dispersion maintains its integrity.
Another object of this invention is to accomplish transfer of a fiber dispersion from the means of its dispersion to a web former, so that this transfer is accomplished uniformly across the width of the former.